Detailed investigations continue on the molecular basis of calcium and phosphate absorption system, and the effect of vitamin D and other factors and conditions on these processes. These include: (a) finalization of the amino acid sequence of the bovine vitamin D-dependent calcium-binding protein (CaBP) and continued studies on its Ca-binding properties and structural modifications by Ca plus 2; (b) continuation of the sequence of the chick vitamin D-dependent calcium-binding protein; (c) isolation, further characterization and localization of vitamin D-responsive integral membrane protein from intestinal brush borders; (d) isloation of basal-lateral membranes with the purpose of characterizing the "Ca-pump", localized on these membranes; (e) continued studies on the phosphate transport system, using isolated chick intestinal cells; (f) investigations on the stimulatory effect of AcBP on brush border CaATPase; (g) isolations and characterization of a newly uncovered cytosol binding protein that forms a Ca plus 2-requiring complex with CaBP; (h) further studies on the calcium-binding proteins in pig intestine and their modification by Ca-dependent diets.